The depth of penetration achieved in continuous wave (CW) laser welding results from a balance of many complicated phenomena, which are linked with the characteristics of the heat source. In this work, the laser welding process has been investigated in terms of basic laser material interaction parameters: power density and interaction time. It has been shown that these two parameters are insufficient to characterize the laser welding process. Thus, a third parameter, specific point energy, has been introduced, which along with the power density and the interaction time allowed the welding process to be uniquely defined. It has been shown that the depth of penetration is mainly controlled by the power density and the specific point energy, whilst the weld width is controlled by the interaction time.